Problem: What do the following two equations represent? $-3x+4y = -4$ $-20x-15y = 5$
Putting the first equation in $y = mx + b$ form gives: $-3x+4y = -4$ $4y = 3x-4$ $y = \dfrac{3}{4}x - 1$ Putting the second equation in $y = mx + b$ form gives: $-20x-15y = 5$ $-15y = 20x+5$ $y = -\dfrac{4}{3}x - \dfrac{1}{3}$ The slopes are negative inverses of each other, so the lines are perpendicular.